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zavikan 10-11-2012 02:32 AM

Water solubility of equilibrium
 
Any of you science heads know/can figure the water solubility limits of equilibrium? I want to make a premix with tap water to use with my spare peristaltic pump...I'm using 1 liter bottles, large dose pumps (66ml a minute).

Blue Falcon 10-11-2012 04:03 AM

That stuff is a pain to get to dissolve. Your best best is to add it to boiling water. Might take you a few tries but basically you need to add the powder, let the water cool, let it sit for about 24 hours and check to see if any fell out of solution (will be a white precipitate on the bottom of the bottle if it falls out of solution). Keep re-boiling and adding more till it falls out of solution. That will tell you how much the liter of water will hold and then you know for the next time you make a fresh bottle.

However, even if you can get it to fully dissolve, it may still drop out of solutions after a few days (weeks?) if you dont keep the water circulated.

Sotty 10-11-2012 04:14 AM

or if the temperature in your house drops.

How much of this solution are you tearing through? I fully understand the desire to get max concentrations to decrease frequency of changeouts. I've never done this personally for a tank. Long ago, I was a chemist and when we very rarely stored inorganic solutions made with solutes with low solubility, such as CaSO4, to near their solubility point. Over time, with temp changes in the room the risk of precipitation was too high. And once you precipitate some out then you have no idea what you are dosing. In the long run this probably wouldn't be the end of the world, but not ideal either.

Have you tried the recommended dilution from Seachem?

or alternatively you could start with 800mL of water (I would go room temp) and get as much to dissolve as possible, keeping track as you go for future batches. Then after just have a couple crystals left on the bottom that won't dissolve top off to an even liter. This should give you just under a 20% safety margin with the solubility that should account for temperature fluctuations, minute amounts of evaporation, etc.

I would not use hot water if you plan on keeping the solution for an extended period of time. There is nothing wrong with using hot water in the future as long as you know that the amount that you put in will stay in solution in room temperature water, but you will be able to get a lot more to go into solution using the hot water. When the solution cools it will become super saturated and will eventually precipitate out.

Sorry I don't have any had numbers, but I have a gH of 8 out of the tap so I've never used the stuff.

Good Luck.


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